The present invention relates to a new and improved pneumatic vehicle tire and, more particularly, to a new and improved pneumatic tire having a radial ply carcass or having a bias ply carcass.
The present invention relates to a pneumatic vehicle tire, especially for commercial vehicles, having a radial carcass, the plies of which are made of steel or of a material of comparable high strength, and the ends of which terminate at or around the tire beads. The tire has a centrally disposed tread strip and a multi-ply belt. Typically, in such a tire, the shoulders or lateral areas of the tire tread tend to wear at a greater rate than the central portion of the tread. This necessitates the premature scrapping of such tires due to their total wear in the shoulder area although the central portion of the tread is still satisfactory for substantial additional service. The severe conditions during the service life of a commercial tire as well as the differing impact of certain forces or stresses on the tire tread across its lateral or widthwise extent significantly contributes to the non-uniform distribution of tread wear.
In an attempt to overcome the drawbacks in presently known tires, it has been suggested to provide a tire specifically having a rubber component of a different property to beneficially affect the tire tread performance. For example, it has been suggested that additional rubber be incorporated in the laterally outward areas of the tread so that both the central and lateral portions of the tread will wear out at approximately the same time, notwithstanding the fact that the laterally outward areas of the tread wear more quickly than the central area. This solution may, however, cause an unwanted weight increase in the shoulder region which increases the heat build-up in the tire, thereby adversely affecting tire life. Moreover, increasing the quantity of material in the shoulder regions adds to the cost of manufacture of the tire.
U.S. Pat. No. 3,853,164 to Mirtain proposes another solution to the problem of disproportionate tread wear. Mirtain discloses a cushion, formed of a material harder than the material of the remainder of the tread, disposed between the tread and the breaker of the tire. The cushion extends to one or both of the lateral or outside walls of the tire. This solution also is not completely satisfactory because the use of such a hard cushion results in a ride quality which is substantially rougher than that of conventional tires. Furthermore, it has been found that the use of such a hard cushion tends to reduce the traction of the tire.
U.S. Pat. No. 4,671,333 to Rohde et al. discloses a tire with a low-damping rubber layer disposed between plies of a multi-ply breaker belt. Such tires achieve their best results when used with commercial vehicles. By providing a step in the shoulder region, by having the belt plies extend laterally into the stepped portions, and by possibly introducing a low-damping rubber layer between plies of the belt, it was hoped to achieve a tire having a reduced resistance to rolling. German Auslegeschrift 10 07 644 to Fletcher discloses a vehicle tire having a belt of steel cord fabric with a resilient rubber underlayer of a carcass rubber mixture disposed radially outwardly from an eight ply diagonal carcass of textile fabric. The belt plies extend at an angle of 45 degrees relative to the circumferential direction of the tire. The rubber underlayer serves to prevent detachment of the belt from the carcass due to the overall rigidity of the tire and the relative movement between the tread strip and the carcass resulting therefrom. The rubber underlayer is at least 2 to 5 mm thick.
U.S. Pat. No. 3,931,844 to Mirtain discloses a pneumatic tire having a cushion-like support under the tread member. The support is more supple, or softer, than the rubber mixture of the tread member. The cushion extends over the tire width and has a greater thickness in the midcircumferential plane region of the tire. The cushion has only a relatively small thickness in the shoulder regions of the tire. The disclosed tire is intended to provide uniform tire wear and improved traction.
Nonetheless, in spite of the attempts to ameliorate the problems of the tire tread performance through the strategic placement of special property rubbers, there still remains room for improvement in this approach to an improved tire.